Injection pump for internal combustion engines

ABSTRACT

An injection pump for an internal combustion engine, has a casing in which a hollow cam shaft carrying at least one pumpoperating cam is rotatably supported. A driving shaft extends within the hollow camshaft, and an axially displaceable coupling sleeve is interposed between the driving shaft and the camshaft. A fluid pressure servocontrol such as an hydraulic annular piston, are housed within said hollow camshaft for controlling axial displacement of the coupling sleeve, the latter having, for example, helicoidal splines, so that displacement of said sleeve axially varies the relative angular position of the camshaft and the driving shaft and thereby the relative timing of the operation of a pumping member operated by the rotation of the camshaft. To assist reliable operation at low pressures the outer diameter of the annular actuator piston should exceed its inner diameter by at least 65 percent.

United States Patent [72] Inventor Giuseppe Sola Turin, Italy [21 1 Appl. No. 855,286

[22] Filed Sept. 4, 1969 [45] Patented Sept. 7, 1971 [731 Assignee FIAT Societa per Azioni Turin, Italy [32] Priority Sept. 28, 1968, Aug. 6, 1969 [33] Italy I 3 1 1 53303 A/68 and 5299s A/9 [54] INJECTION PUMP FOR INTERNAL COMBUSTION ENGINES 8 Claims, 6 Drawing Figs.

52 us. Cl 154/25, 123/139 AP [51] Int.Cl Fl6d 5/00, F02m 39/00 [50] Field of Search 74/840;

[56] References Cited UNITED STATES PATENTS 2,372,180 3/1945 Edwards 123/1391 X 31 33 269 @9 sea 5t Primary Examiner-Martin P. Schwadron Assistant Examiner Barry Grossman Attorney-Sughrue, Rothwell, Mion, Zinn & Macpeak ABSTRACT: An injection pump for an internal combustion engine, has a casing in which a hollow cam shaft carrying at least one pump-operating cam is rotatably supported. A driving shaft extends within the hollow camshaft, and an axially displaccable coupling sleeve is interposed between the driving shaft and the camshaft. A fluid pressure servocontrol such as an hydraulic annular piston, are housed within said hollow camshaft for controlling axial displacement of the coupling sleeve, the latter having, for example, helicoidal splines, so that displacement of said sleeve axially varies the relative angular position of the camshaft and the driving shaft and thereby the relative timing of the operation of a pumping member operated by the rotation ofthe camshaft. To assist reliable operation at low pressures the outer diameter of the annular actuator piston should exceed its inner diameter by at least 65 percent.

Fig. 1

PAIENTEDsEP 7l97l 3.603112 saw u or 6 INJECTION PUMP FOR INTERNAL COMBUSTION ENGINES This invention relates to an injection pump for an internal combustion engine.

Injection pumps are known in which injection-timing means are interposed between a driving shaft and a cam driven thereby. Operation of the kg./sq. cm. means to vary the relative angular position of the driving shaft, which is enginedriven, and the cam is generally effected by hydraulic servocontrol means in dependence upon the rotary speed of the pump.

Injection pumps of the above-mentioned type are known, in which the injection-timing means and the hydraulic servocontrol are arranged within a hollow cam-carrying body and supported by the pump-driving shaft.

Such known pumps should operate at high speed and generate very high injection pressures up to 700-1000 kg./sq. cm. in order to meet the requirements of modern fuel-injection engines. Consequently the thrusts acting on the cam can reach and exceed 800 kg., and the cam is supported on at least one side by the driving shaft through the interposition of a coupling sleeve coupledwith the shaft and cam by helical and axial splines respectively, or by splines which are both helical: axial displacement of the sleeve can then effect changes in the relative angular positions of the cam and the driving shaft, for injection-timing purposes.

The high cam loads result in a high resistance against axial movement of the sleeve. Such resistance obviously adversely affects the operation of the injection timer. Moreover, this drawback cannot in practice be remedied by displacing the sleeve by means of a servocontrol, control, since the limited space available is in general insufficient to a accommodate a servocontrol of sufficient power.

With injection pumps having a single pumping member, the rotation of a multiple-lobe cam is commonly converted to reciprocating movement of the pumping member with the aid of a desmodromic gear devoid of resilient means for maintaining contact with the cam surface: it is in this case essential for the axis of rotation of the cam to be maintained coaxial with the axis of the driving shaft. Obviously, where the pump has a single pumping member and does not employ a desmodromic gear, it does not meet the requirement for accurate coaxial positioning mentioned above, which adversely affects the operation of the injection pump.

An object of this invention is to provide an injection pump for internal combustion engines avoiding the above-mentioned disadvantages.

Accordingly the injection pump of the present invention has at least one rotary pump-operating cam and is characterized by the following features in combination:

a. the cam is carried by a hollow body which is driven from a driving shaft extending into said hollow body and connectable to a rotary drive input at one end;

b. The pump incorporates injection-timing means including an axially displaceable coupling member arranged between the hollow cam-carrying body and the driving shaft, said coupling member being effective upon axial displacement to vary the relative angular position of said body and said shaft;

c. fluid pressure servocontrol means are provided within the hollow cam-carrying body to vary the axial position of the coupling member in dependence upon the rotary speed of the driving shaft, and

d. the hollow cam-carrying body is supported for rotation directly in the pump casing.

Preferably the driving shaft, which is adapted for connection to a drive input at one end, is supported within the hollow cam-carrying body in proximity to said one end by an annular support and is supported directly at its other end in the bore of said hollow cam-carrying body.

Preferably the pump includes a centrifugal governor housed within the hollow cam-carrying body and controlling the supply of pressure fluid to said servocontrol means in dependence on the rotary speed of said body. The centrifugal governor is preferably housed in a chamber formed in one end of the hollow cam-carrying body between an enlarged head of the driving shaft and a hub closing said end of the body and drivingly connected thereto, said hub carrying adapter means for connection to a speed governor of the engine.

The coupling member preferably comprises a sleeve having internal and external spline connections to the driving shaft and to the hollow cam-carrying body respectively, at least one of said splined connections being helicoidal.

A preferred feature of the pump according to the invention is that the servocontrol means include an annular piston mounted for sliding movement on a part of the driving shaft and bearing against one end of the coupling member to effect axial displacement thereof. The annular piston is, additionally, preferably controlled by the action of a spring which biases the piston away from the head of the driving shaft.

It is particularly desirable to ensure reliable and regular operation of the injection-timing means even when the pressure of the working fluid (e. g. oil) acting on the annular piston is low. Also, it is desirable to avoid the situation where even at high working fluid pressures, registered when the engine runs at, or even exceeds, its maximum rated speed, the coupling member is still directly engaged by the annular piston on which the fluid pressure continues to act, so that a heavy load builds up on a stop intended to limit the axial movement of the driving shaft.

According, therefore, to a preferred embodiment of the invention the outer diameter of the annular piston exceeds its inner diameter by at least 65 percent, and is preferably twice the inner diameter. In addition, the hollow cam-carrying body may be provided with a shoulder which acts as a stop limiting movement of the annular piston under the action of the pressure fluid.

Yet another desideratum in practice is to provide a pump including injection-timing means made up of unified components parts, regardless of whether the injection pump has one or several lobed cams supported by a common cam-carrying hollow body.

Preferably the interior cavity of the driving shaft containing components of the servocontrol means is accessible from outside to enable an indication to be obtained, while the pump is working, regarding the advance or relative angular position of the cam and the driving shaft in terms of the number of revolutions of the driving shaft.

Thus the hub closing end of the cam-carrying body may have an axial bore communicating with a coaxial bore in a sleeve on which a member is mounted for axial movement under the action of the governor.

The annular piston is preferably mounted on a part of the driving shaft opposite a head of enlarged diameter supported within a corresponding portion of the bore in the hollow camcarrying body. The outer diameter of the annular piston may then be equal to or greater than the outer diameter of said driving shaft head.

It follows from this that the diameter of the annular piston can be equal to or greater than the diameter of the hub which preferably closes one endof the hollow cam-carrying body so that in any case the outer diameter of the annular piston will always be greater than the outer diameter of the coupling member.

Further characteristic features of the invention will be apparent from the following description, given by way of example only, with reference to the accompanying drawings, in which:

FlG. 1 is a cross-sectional view on line 1-! of FIG. 2 of an injection pump according to one embodiment of the invention, having a single multiple-lobed cam;

FIG. 2 is an axial sectional view in two orthogonal planes on line II-ll of FIG. 1;

FIGS. 3 and 4 are cross-sectional views on lines III-Ill and IVIV respectively in FIG. 2;

FIG. 5 is a diagrammatic side elevational view of a multiplelobe cam and its respective supports for an injection pump according to the invention, of the type having three axially spaced-apart cam lobes, and

FIG. 6 is an axial sectional view in a single plane of an injection pump according to another embodiment of the invention.

Corresponding parts are denoted by the same reference numerals throughout the figures.

In the injection pump shown in FIGS. 1 to 4 a cam 10 having six peripheral lobes is secured to a hollow cam-carrying body comprising a hollow cam shaft 11 and is enclosed within the main casing 12 of the pump. The parts of the cam shaft 11 on opposite sides of the cam 10 have substantially equal diameters. The casing 12 has secured thereto at one end a cover 13 enclosing a speed governor 14 for the engine (not shown) in connection with which the injection pump is employed.

The cam 10 efiects displacement of a single pumping member (not shown) through the interposition of a desmodromic mechanism of known type, including inter alia a beam 16 (FIG. 3) pivotally mounted on a spindle 17 the axis of which is parallel to the axis of the cam shaft 11. A cam-follower roller 18 is rotatably mounted on an axle 19 carried at one end of the beam 16, the roller 18 engaging the circumferential surface 100 of the cam 10. At its other end the beam 16 is formed with a convex surface 20 also contacting the circumferential surface 10:: of the cam 10.

The hollow cam shaft 11 is mounted for rotation on two bearing supports. One bearing support is formed by an internal cylindrical bore 21 in the casing 12 of the pump; the other bearing support is formed by a cylindrical bore 22 in the cover 13 and extends into the interior of the casing 12. The two bearing surfaces 21, 22 are lubricated by oil under pressure supplied to respective annular grooves 23, 24 in the bearing surfaces. Antifriction bearing means may be utilized instead of the plain bearing surfaces illustrated.

The hollow camshaft II is formed on the side of the bore 21 remote from the cover 13 with an external annular circumferential row of teeth 1 1a meshing with a corresponding set of teeth on a toothed wheel 25, FIG. 4, which transmits rotational drive from the shaft 11 to a distributor (not shown) of the pump.

The camshaft 11 houses a coaxial driving shaft 26 provided at one end with an adapter 26a for connection to a rotary drive input, that is, a power takeoff from the engine. The end adapter 26a extends axially outwardly from the shaft 1 l and is supported in proximity to the adjacent end of the shaft 11 through the interposition of an annular support 27 positioned by a circlip 28. The other end of the driving shaft 26, which is directly supported by the hollow camshaft 11, comprises a head 26b which is larger in diameter than said one end and defines, together with a hub 29 formed on a rotary shaft 29a a chamber 30 accommodating spherical masses 31 of a small centrifugal governor. As shown in FIG. 2, the cam shaft 11 is directly keyed to the hub 29. The shaft 290 is provided with a screw adapter 29b for effecting a drive connection to the speed governor 14. The masses 31 are carried along in rotation by radial wings 32 formed in the face of the hub 29 turned towards the driving shaft 26. The masses 31 cooperate with an inclined fru stoconical surface 33 of a plate 35 which has a hub 35b slidably mounted on a sleeve 34 for movement in the direction of the common axis of the driving shaft 26 and the camshaft 1 l.

The plate 35 abuts a distributor slide 36 having a central through bore. The slide 36 is arranged in the central bore 26c of the shaft 26 which communicates with the chamber 30. The

slide 36 is biased in the direction of the chamber 30 by a which groove 24 is supplied with oil under pressure from the connection 41.

An axially extending conduit 42 is provided in the driving shaft 26 and connects near the annular support 27 with radial outlets 43 opening into an annular chamber 44 defined in part by an annular recess on the face of the support 27 remote from the circlip 28. The chamber 44 is sealed by an annular piston 45 movable axially on the shaft 26 and mounted for sliding movement in a cylindrical portion 11b of the bore of the hollow camshaft 11. The piston 45 bears against one end of coupling sleeve 46, the latter being biassed against the piston 45 by a helical spring 47 interposed between the head 26b and the sleeve 46.

The distributor slide 36 is provided with a circumferential annular groove 36a which controls -by axial movement of the slide intercommunication between an annular groove interconnecting the radially inner ends of the conduits 39 and a drilling in the wall of the bore 260 communicating with the conduit 42.

The coupling sleeve 46 is coupled to the camshaft 1 1 by external axially extending splines meshing with the axial splines in a bore portion of the shaft 1 l of reduced diameter. The sleeve 46 is coupled to the driving shaft 26 close to the head 26b by internal splines, 49, extending helically. A transverse pin 50 extends radially through a longitudinally extending diametrically opposed slots 51 in the shaft 26 and is axially slidable with the sleeve 46, one end of the pin 50 sliding along a portion 1 1c of the bore of the hollow camshaft between axially extending splines of the said bore. The cylinder 38 which acts as a movable stop for the spring 37, bears on the pin 50. Alternatively, the sleeve 46 may be coupled to the camshaft 11 by helicoidal splines and may be coupled to the driving shaft 26 by axial splines. Or again, the sleeve 46 may be coupled to both the shaft 11 and the shaft 26 by helicoidal splines.

During operation of the pump the driving shaft 26 is driven from the engine through the adapter 26a and transmits rotation to the camshaft 1 1 and hence to the multiple-lobe cam 10 through the intermediary of the coupling sleeve 46. The sleeve 46 may be subjected to axial displacement to the left (as viewed in FIG. 2) by the action of the annular piston 45 when oil under pressure is supplied to the annular chamber 44. The extent of such movement of the piston 45 is proportional to the speed of revolution of the pump: upon increase in the speed of the pump the distributor slide 36 is displaced, to the right (as viewed in FIG. 2), against the action of the spring 37 and permits interconnection of the conduits 39 and 42, through the groove 360, which intercommunication ceases as soon as the slide 36 is returned under the loading of thespring 37; upon a lowering in the rotational speed of the pump the slide 36 is displaced to the left under the action of the spring 37, the radial surface of the plate 35 uncovering an end of the conduit 42 to connect said conduit 42 to exhaust through the chamber 30.

Rotation of the coupling sleeve 46 relative to the driving shaft 26 is prevented by the engagement of the pin 50 in the diametrically opposed slots 51 in the sleeve 46. By virtue of the helicoidal splines the angular position of the camshaft l1, and, therefore, of the cam 10, relative to the driving shaft 26, is dependent upon the axial position of the coupling sleeve 46, and thus upon the speed of the pump.

An advantage of the above-described structure is that the mass of the rotary cam 10 is directly connected with the rotary mass of the speed governor 14 for the engine. The coupling sleeve 46 transmits drive from the driving shaft 26 to the camshaft 11: the axial displacement of the coupling sleeve 46 by means of the piston 45 constantly subjected to the action of the pressure oil assists in damping any oscillation, making the injection timer irreversible in action.

It will be clear from the above description and drawings that this invention provides an injection pump incorporating a centrifugal governor of considerable size within the hollow cam carrying body. This governor affords an efficient control in the distributor slide and additionally provides for variation of the injection timing within wide limits. The shaft 11 of the pump may be driven at one half the rotation speed of the drive shaft of the engine with which the pump is associated.

The characteristics of the centrifugal governor operating the distributor slide 36 may be easily varied in order to meet the requirements of different engines by either modifying the action of the spring 37, for example by changing the spring 37, or by modifying the shape of the surface 33 with which the spherical masses 31 of the governor cooperate.

Any replacement of the spherical masses 31 of the governor or the spring 37 acting on the distributor slide 36 is facilitated by the arrangement of these parts in the chamber 30 closed by the hub 29, since the speed governor 14 of the engine and the hub 29 may easily be released from the hollow camshaft 1 l to give access to the chamber 30.

In the diagrammatic representation of FIG. 5 a tubular camshaft 52 provided with three lobes 53, 54, 55 respectively, is supported in the casing (not shown) of an injection pump through the interposition of supports, denoted diagrammatically by 56 and 57, positioned externally of the lobes of the camshaft 52. A driving shaft (not shown) extends with the camshaft 52, having an end adapter 26a extending axially beyond one end of the camshaft 52 for power takeoff from the engine (not shown).

Means are arranged between the driving shaft 26 and camshaft 52 for varying the injection timing and its respective servocontrol means, which are not visible in the elevational view in FIG. 5.

The speed governor 14 (shown in broken outline) for the engine is arranged at the end of the camshaft 52 remote from the power takeoff adapter 26a of the driving shaft, the governor 14 being coupled to a screw end adapter 29a fast with camshaft 52.

Obviously, with the arrangement shown in FIG. 5 the means adapted to vary the injection timing and its respective hydraulic servocontrol means are not affected by the thrusts acting on the cams 53-55 during operation of the injection pump, which thrusts are directly discharged on the pump casing through the supports 56 and 57.

FIG. 6 illustrates an injection pump according to a modification of that shown in FIGS. 1 to 4. Components of the pump of FIG. 6 which correspond to those of the pump of FIGS. 1 to 4, and which are indicated by the same reference numerals, have the same arrangement and functions and will not be described further.

In the embodiment of FIG. 6 the shaft 29a and its hub 29 are traversed by an axial through bore 290 communicating with the bore of the sleeve 34 facing towards the head 26b. The sleeve 34 terminates a short distance from the adjacent radial end face 26c of the head 26b.

The cylinder 38, which acts as a stop for the spring 37, has a forked end 38a in which is received the transverse pin 50 which traverses the bore 260 of the hollow driving shaft 26. The pin 50 extends through the diametrically opposed longitudinally extending slots 51 in the shaft 26 to effect a rotary drive connection with the shaft 26.

The annular piston 45 is sealed in the bore portion 1 lb by a sealing ring 45a located in an annular groove on the outer circumferential surface of the piston 45. The piston 45 has an outer diameter which is substantially equal to that of the head 26!) of the driving shaft 26. Movement of the piston 45 towards the head 26b is restricted by an annular stop shoulder formed by a lateral face of a stop ring 60. The ring 60 is housed in an annular groove formed in a portion of the bore of the hollow camshaft 11 between the bore portion 11b in which the piston 45 slides and the intermediate bore portion 1 lc,of a lesser diameter than the portion 1lb,in which the splines meshing with the sleeve splines 48 are formed.

It will be apparent that in the embodiment of FIG. 6, even when coil is fed into the chamber 44 under high pressure (for example when the engine is running at its maximum rated speed or at an even higher speed) the piston 45 cannot impart an abnormally high axial load to the driving shaft 26. Consequently, a heavy load cannot build up on the radial abutment which is intended to restrict the end float of the driving shaft 26 within the hollow camshaft 1 l, and which consists of the radial face of a disc element 61 held in position by a resilient locking ring 62. The disc element 61 abuts the adjacent end of the camshaft l1 and restricts movement of the shaft 26 axially away from the drive input adapter 26a.

It can also be seen that in the embodiment of FIG 6 the bore 260 of the driving shaft 26 is at'all times in'communication with the exterior by means of the central bore of the distributor slide 36, the bore of the sleeve 34 and the bore 290 of the hub 29 and the shaft 29a. Through these coaxial bores a drive-transmitting element 63 can be introduced to engage the cylinder 38 so as to show the effective variations of the advance governor in terms of revolutions of the cylinder 38 (transmitted from the driving shaft 26 through the pin 50) or alternatively to regulate from without the stroke of the coupling sleeve 46 in'order to restrict, or to exclude entirely, the advance introduced thereby.

Additional applications of the element 63 include its use to regulate preloading of the spring 37, or its use for providing a drive output from the driving shaft 26 in order to perform several functions, for example correction of the delivery of the pump in relation to the number of revolutions of the engine.

The hub plate 29 in the embodiment of FIG. 6 is held in position by an externally threaded ring nut 64 screwed into internal screw threading on the internal surface 67 of an annular wall portion 11d of the bore of the camshaft ll of greater diameter than the portion of said bore in which the head 26b is accommodated. The ring nut 64 is provided on its internal surface with axial splines 64a which mesh with external axial splines 6511 of a locking ring 65. The internal edge of the locking ring 65 is provided in turn with projections 65b which engage in corresponding notches 56 in the hub 29 close to the latter.

In the embodiment of FIG. 6 it is possible to give the piston 45 a large useful surface area exposed to the action of the pressurized oil in the chamber 44 so as to guarantee reliable and regular action of the advance variator even when the oil pressure is low, for example at a rotary speed of the camshaft l 1 corresponding to operation of the engine in lst gear.

The parts are in practice preferably so proportioned that the outer diameter of the annular piston 45 is at least 65 percent greater than its inner diameter, and can without difficulty be twice the inner diameter.

In the example illustrated in FIG. 6, the outer diameter of the piston 45 is equal to the diameter of the head 26b of the driving shaft 26, but it can be equal to or even greater than the outer diameter of the hub 29.

What is claimed is:

l. A fuel-injection pump for an internal combustion engine including a hollow casing, bearing means in said casing and an automatic hydraulic timing device rotatably supported by said bearing means, wherein said automatic device comprises in combination:

a. a tubular cam-carrying body mounted for rotation directly in the pump casing;

b. at least one pump-operating cam carried on the outer periphery of said tubular shaft;

c. a driving shaft extending into said tubular body and being formed with a head arranged near one end of said body and mounted for rotation directly in said body and with a portion smaller in diameter than the inner bore of said body provided with an adapter for connection to a rotary drive input extending beyond the other end of said body;

d. means acting directly between said tubular cam-carrying body and said driving shaft for preventing any relative axial displacement of said body and shaft;

e. anannular support in the bore in said tubular body in proximity of said other end of said body and rotatably supporting the driving shaft near said adapter, said annular support defining, together with the tubular body the drive shaft and the respective head, an axially extending annular chamber;

f. injection-timing means including an axially displaceable coupling member arranged in said annular chamber in the form of a sleeve provided with internal and external splined connections to the driving shaft and the tubular body respectively, at least one splined connection being helical;

g. fluid pressure servocontrol means within said tubular body to vary the axial position of said sleeve, said servocontrol means including an annular piston mounted for sliding movement on the part of the driving shaft arranged between said sleeve and said annular support and bearing against the end of said sleeve facing said support to effect axial displacement thereof;

h. a centrifugal governor, controlling the supply of pressure fluid to said servocontrol means dependently upon the rotary speed of the driving shaft, housed in the bore in the tubular body between the head of the drive shaft and a cover closing said one end of the tubular body.

2. Pump as claimed in claim 1, wherein said means for preventing any mutual axial displacement of said tubular body and driving shaft comprises a retaining ring secured in one end of the tubular body and a radial shoulder facing said ring and formed inside the inner bore in said body, both abutting outer marginal portions of the opposite faces of said head formed on the driving shaft.

3. Pump as claimed in claim 1, wherein said means for preventing any mutual axial displacement of said tubular body and driving shaft comprises a radial shoulder facing said cover and formed inside the inner bore in said body and an annular element which abuts the end of the tubular body opposite said cover and a locking ring attached to the portion of the driving shaft adjacent the respective end adapter, and holding said annular element in place.

4. Pump as claimed in claim 1, wherein the outer diameter of said annular piston exceeds its inner diameter by at least 65 percent.

5. Pump as claimed in claim 1, wherein the outer diameter of said annular piston is twice its inner diameter.

6. Pump as claimed in claim 1, wherein the outer diameter of the annular piston is equal to or greater than the outer diameter of the said head of the driving shaft.

7. Pump as claimed in claim 1, wherein the internal surface of the hollow cam-carrying body is provided with a shoulder which acts as a stop limiting movement of the annular piston under the action of the pressure fluid.

8. Pump as claimed in claim 7, including a ring received in a part of the bore of the cam-carrying body and having a lateral face defining said stop. 

1. A fuel-injection pump for an internal combustion engine including a hollow casing, bearing means in said casing and an automatic hydraulic timing device rotatably supported by said bearing means, wherein said automatic device comprises in combination: a. a tubular cam-carrying body mounted for rotation directly in the pump casing; b. at least one pump-operating cam carried on the outer periphery of said tubular shaft; c. a driving shaft extending into said tubular body and being formed with a head arranged near one end of said body and mounted for rotation directly in said body and with a portion smaller in diameter than the inner bore of said body provided with an adapter for connection to a rotary drive input extending beyond the other end of said body; d. means acting directly between said tubular cam-carrying body and said driving shaft for preventing any relative axial displacement of said body and shaft; e. an annular support in the bore in said tubular body in proximity of said other end of said body and rotatably supporting the driving shaft near said adapter, said annular support defining, together with the tubular body the drive shaft and the respective head, an axially extending annular chamber; f. injection-timing means including an axially displaceable coupling member arranged in said annular chamber in the form of a sleeve provided with internal and external splined connections to the driving shaft and the tubular body respectively, at least one splined connection being helical; g. fluid pressure servocontrol means within said tubular body to vary the axial position of said sleeve, said servocontrol means including an annular piston mounted for sliding movement on the part of the driving shaft arranged between said sleeve and said annular support and bearing against the end of said sleeve facing said support to effect axial displacement thereof; h. a centrifugal governor, controlling the supply of pressure fluid to said servocontrol means dependently upon the rotary speed of the driving shaft, housed in the bore in the tubular body between the head of the drive shaft and a cover closing said one end of the tubular body.
 2. Pump as claimed in claim 1, wherein said means for preventing any mutual axial displacement of said tubular body and driving shaft comprises a retaining ring secured in one end of the tubular body and a radial shoulder facing said ring and formed inside the inner bore in said body, both abutting outer marginal portions of the opposite faces of said head formed on the driving shaft.
 3. Pump as claimed in claim 1, wherein said means for preventing any mutual axial displacement of said tubular body and driving shaft compriSes a radial shoulder facing said cover and formed inside the inner bore in said body and an annular element which abuts the end of the tubular body opposite said cover and a locking ring attached to the portion of the driving shaft adjacent the respective end adapter, and holding said annular element in place.
 4. Pump as claimed in claim 1, wherein the outer diameter of said annular piston exceeds its inner diameter by at least 65 percent.
 5. Pump as claimed in claim 1, wherein the outer diameter of said annular piston is twice its inner diameter.
 6. Pump as claimed in claim 1, wherein the outer diameter of the annular piston is equal to or greater than the outer diameter of the said head of the driving shaft.
 7. Pump as claimed in claim 1, wherein the internal surface of the hollow cam-carrying body is provided with a shoulder which acts as a stop limiting movement of the annular piston under the action of the pressure fluid.
 8. Pump as claimed in claim 7, including a ring received in a part of the bore of the cam-carrying body and having a lateral face defining said stop. 